Impact of Fluorine Substitution on the Ultrafast Dynamic Processes of Coumarin Molecules
The development of highly efficient,photostable,and eco-friendly fluorescent dyes is currently a prominent focus in scientific research,attracting significant attention.Recent studies have emphasized Twisted Intramolecular Charge Transfer(TICT)'s crucial role in determining fluorescent dyes'luminescence efficiency.Consequently,effectively suppressing the TICT process is imperative for progressing fluorescent markers and probes.Among the various fluorescent dyes,coumarin and its derivatives,particularly 7-amino coumarin dyes,have gained significant recognition as extensively utilized constituents in diverse systems owing to their robust fluorescence and prolonged fluorescence lifetimes.Nevertheless,previous examinations have predominantly concentrated on the effect of different solvents on the excited-state behavior of coumarin dye molecules,overlooking the significant influence of dye molecule structure on the TICT process.This study utilized a combination of femtosecond time-resolved transient absorption(TA)spectroscopy and density functional theory(DFT)calculations to gain deeper insights into the excited-state dynamics of coumarin dyes C460 and C481 in various solvents.The results revealed that C481 predominantly undergoes the TICT process in highly polar methanol solvents with strong hydrogen-bonding capabilities.Furthermore,quantum chemical calculations indicated that introducing fluorine substitutions reduces the molecules'internal torsional barriers,leading to enhanced non-radiative deactivation processes and,consequently,more pronounced fluorescence quenching phenomena.This investigation provides insights into the selection of suitable solvents for optimizing the performance of fluorescent dyes and offers valuable guidance for their design.
Transient absorption spectroscopyTwisted intramolecular charge transferDensity functional theory
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